Ground compaction

ABSTRACT

The apparatus ( 10 ) is a weighted body ( 12 ). The first regions ( 20 ) taper at a first taper angle, such as 5°. Second regions ( 22 ) taper at a greater angle, such as 60°. The ground is compacted by dropping the apparatus ( 10 ) on the ground, so that the nose ( 18 ) penetrates the ground. The relatively low taper angle of the first regions ( 20 ) tends to result in deeper penetration. The relatively high taper angle of the regions ( 22 ) tends to create some bounce on impact, helping to free any tendency for the first regions ( 20 ) to stick. The second regions ( 22 ) also create greater downward compaction.

This application is based on GB 0712329.2 filed with United KingdomPatent Office on Jun. 26, 2007, the entire content of which isincorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to improvements in or relating to methodsand apparatus for ground compaction.

SUMMARY OF THE INVENTION

Embodiments of the invention provide ground compaction apparatuscomprising:

a weighted ground impact body with an outer surface which reduces inwidth to a nose;

the outer surface having a plurality of first regions which taper at afirst taper angle, and

at least one second region between first regions, the second regiontapering at a second taper angle which is greater than the first taperangle.

The body may be generally conical. The body may be substantiallycircular in section. The body may be substantially polygonal in section.The body may be substantially hexagonal or octagonal in section.

The or each second region may be a band around the body.

Each first region may be a band around the body. At least one firstregion may be separated from a neighbouring first region by a bandproviding a second region.

There may be a plurality of second regions. The spacing of secondregions may be non-uniform. The second regions may be spaced moreclosely nearer the nose than further from the nose.

The radial extent of the or each second region may be substantiallyequal to the radial extent of a neighbouring first region.

The first taper angle may be in the range 0° to 15°. The first taperangle may be substantially 5°. The second taper angle may be greaterthan 45°. The second taper angle may be substantially 60°.

The weight of the body may be at least 1 tonne and may be 12 tonnes ormore.

Embodiments of the invention also provide a method of ground compaction,in which a ground compaction apparatus as defined above is dropped ontothe ground to be compacted.

BRIEF DESCRIPTION OF THE DRAWINGS

Examples of the present invention will now be described in more detail,by way of example only, and with reference to the accompanying drawings,in which:

FIG. 1 is an elevation of ground compaction apparatus in accordance withone embodiment of the present invention;

FIG. 2 is a simplified, diagrammatic section through the apparatus ofFIG. 1;

FIG. 3 is a diagram illustrating taper angles;

FIG. 4 is an enlarged partial view corresponding with FIG. 2,illustrating ground compaction forces; and

FIG. 5 is a diagrammatic view of the apparatus in use.

DETAILED DESCRIPTION

The drawings illustrate an example of ground compaction apparatus 10.This may be used, for example, for preparing ground prior to buildingwork, foundation work, piling or other operations. It may also be usedas a foundation element in its own right, for example as a stanchionbase.

The apparatus 10 comprises a weighted ground impact body 12. This ismounted to the underside of a plate 14 which carries lifting eyes 16 onits upper surface, allowing the apparatus 10 to be slung from liftingapparatus, for use.

The body 12 has an outer surface which reduces in width to a noseindicated generally at 18, as can be seen in FIG. 1.

The outer surface has a plurality of first regions 20, and secondregions 22. The first regions 20 taper at a first taper angle (asdefined below). The second regions 22 are located between first regions20 and taper at a second taper angle. The second taper angle (of thesecond regions 22) is greater than the first taper angle (of the firstregions 20).

FIG. 2 illustrates the shape of the apparatus 10 more diagrammatically,for ease of understanding of the geometry. The apparatus 10 has acentral axis 24, which is normally vertical during use, andperpendicular to the plate 14, which is normally horizontal in use. Thesection of the apparatus 10, taken perpendicular to the axis 24, has thesame shape at any position along the axis 24, such as at the sectionline X-X in FIG. 2. The section may be substantially circular orsubstantially polygonal, such as substantially hexagonal orsubstantially octagonal. Accordingly, the sectional shape, together withthe width reduction toward the nose 18, gives the apparatus 10 agenerally conical form.

Each first region 20 is a band around the body 12, centred on the axis24. Each second region 22 is similarly a band around the body 12,centred on the axis 24. First regions 20 and second regions 22 alternatealong the axis 24, from the plate 14 to the nose 18. Accordingly, eachfirst region 20 is separated from a neighbouring first region 20 by aband providing a second region 22. There is a plurality of secondregions 22 between the plate 14 and the nose 18. The axial spacing ofsecond regions 22, along the axis 24, is not uniform, as can be seenfrom FIG. 1. The second regions 22 are axially spaced more closelynearer the nose 18 than further from the nose 18.

The radial extent of each second region 22 (that is, the difference inradius, from the axis 24, of the outermost extremity of the region 22and the innermost extremity of the region 22) is substantially equal tothe radial extent of each neighbouring first region 20.

Each region 20, 22 has a taper angle relative to the axis 24. A taperangle is diagrammatically illustrated in FIG. 3. In FIG. 3, the surfaceof a region 20, 22 is illustrated by dotted lines 26 to either side ofthe axis 24. Lines 28, parallel with the dotted lines 26, intersect theaxis 24 at a point 30. An angle 32 can be drawn to either side of theaxis 24, between the axis 24 and one of the lines 28. The angle 32 isthe same to either side of the axis 24. The angle 32 is here termed thetaper angle of the surface indicated by the lines 26.

Returning to FIG. 2, the surface of one first region 20 is continued bya dotted line 34 until intersecting the central axis 24. Similarly, thesurface of one second region 22 is continued by a long dotted line 36.It can readily be seen from FIG. 2 that the taper angle of the firstregion 20 is smaller than the taper angle of the second region 22. Inexamples, the first taper angle may be in the range between 0° and 15°.In one example, the taper angle of the first regions 20 is substantially5°. The taper angle of the second regions 22 is, in one example, greaterthan 45° and may be substantially 60°. Accordingly, when the apparatus10 is hanging with the axis 24 vertical, the surfaces of the firstregions 20 are closer to the vertical than to the horizontalorientation, while the second regions 22 are oriented closer to thehorizontal than the vertical orientation.

In use, the apparatus 10 is lifted above the ground and then droppedonto the ground, penetrating the ground by virtue of the generallytapered shape, and causing ground compaction by the impact. Thecompaction forces which result are schematically illustrated in FIG. 4.In impacts between a dropped body and the ground, impact forces cangenerally be considered as being perpendicular (normal) to the surfaceof the body. Accordingly, two orientations of compaction forces arise.Compaction forces 38 a are closer to the horizontal than to the verticalorientation and arise from the first regions 20 impacting the ground 40around the apparatus 10. Second impact forces 38 b are closer to thevertical than to the horizontal and arise from impact of the secondregions 22 with the ground 40.

When the apparatus 10 is dropped onto the ground 40, the ground 40 issubjected to compaction forces at both of these angles 38 a, 38 b, asillustrated schematically in FIG. 5.

The apparatus 10 described above is expected to provide enhanced groundcompaction performance, for reasons which may include the following. Ifa simpler apparatus is envisaged, with a surface which has a constanttaper angle, then the apparatus will have a short, squat conical form inthe event of a large taper angle, or a long, thin conical form in theevent of a small taper angle. Using a small taper angle results in deeppenetration into the ground, so that compaction is achieved at deeperlevels. However, a long cone with small taper angle is prone to stickingin some ground conditions. Friction between the surface of the cone andthe surrounding ground may grip the weight, hindering removal for afurther dropping operation.

In an alternative with a large taper angle, the impact surface is closerto the horizontal, creating enhanced downwardly directed compactionforces and also tending to provide some bounce at the time of impact,which helps prevent the apparatus sticking in the ground. However, theshorter, squatter form tends to result in less penetration and less deepground compaction.

In the examples described above, the relatively low taper angle of thefirst regions 20 result in a long cone which provides deep penetration.However, the greater taper angle of the second regions 22 creates somebounce on impact, helping to free the first regions 22 to prevent theapparatus 10 sticking. The second regions 22 also create greaterdownward compaction. Accordingly, it is desirable to have the secondregions 22 spaced more closely nearer the nose 18 than further from thenose 18, so that there is a greater contribution to downward compaction,at the greater penetration depth.

In use, it is envisaged that the apparatus 10 will be lifted by asuitable crane 42 (FIG. 5). The crane 42 may be purpose built or generalpurpose. The apparatus 10 is then dropped to penetrate into the ground40 and create compaction, as has been described. The apparatus 10 may bedropped once or repeatedly at the same position. In many situations, anarea of ground may be treated by using the apparatus 10 at differentpoints across the ground, such as at lattice points of a square grid, orother geometry.

In the example described above, the total weight of the apparatus 10 maybe in the region of at least 1 tonne and may be as much as 12 tonnes ormore. The length of the apparatus 10 along the axis 24 may beapproximately 3 m. The diameter of the body 12, at the plate 14, may beapproximately 2 m or more.

Many variations and modifications can be made to the apparatus describedabove, without departing from the scope of the present invention. Inparticular, many different weights, heights, widths, taper angles,dimensions and relative dimensions can be chosen, particularly accordingto the degree of compaction required, the nature of the ground beingcompacted, and the like.

Whilst endeavouring in the foregoing specification to draw attention tothose features of the invention believed to be of particular importanceit should be understood that the Applicant claims protection in respectof any patentable feature or combination of features hereinbeforereferred to and/or shown in the drawings whether or not particularemphasis has been placed thereon.

1. Ground compaction apparatus comprising: a weighted ground impact bodywith an outer surface which reduces in width to a nose; the outersurface having a plurality of first regions which taper at a first taperangle, and at least one second region between first regions, the secondregion tapering at a second taper angle which is greater than the firsttaper angle.
 2. Apparatus according to claim 1, wherein the body isgenerally conical.
 3. Apparatus according to claim 1, wherein the bodyis substantially circular in section.
 4. Apparatus according to claim 1,wherein the body is substantially polygonal in section.
 5. Apparatusaccording to claim 4, wherein the body is substantially hexagonal oroctagonal in section.
 6. Apparatus according to claim 1, wherein the oreach second region is a band around the body.
 7. Apparatus according toclaim 1, wherein each first region is a band around the body. 8.Apparatus according to claim 1, wherein at least one first region isseparated from a neighbouring first region by a band providing a secondregion.
 9. Apparatus according to claim 1, wherein there are a pluralityof second regions.
 10. Apparatus according to claim 9, wherein thespacing of second regions is non-uniform.
 11. Apparatus according toclaim 10, wherein the second regions are spaced more closely nearer thenose than further from the nose.
 12. Apparatus according to claim 1,wherein the radial extent of the or each second region is substantiallyequal to the radial extent of a neighbouring first region.
 13. Apparatusaccording to claim 1, wherein the first taper angle is in the range 0°to 15°.
 14. Apparatus according to claim 13, wherein the first taperangle is substantially 5°.
 15. Apparatus according to claim 1, whereinthe second taper angle is greater than 45°.
 16. Apparatus according toclaim 15, wherein the second taper angle is substantially 60°. 17.Apparatus according to claim 1, wherein the weight of the body is atleast 1 tonne.
 18. Apparatus according to claim 17, wherein the weightof the body is at least 12 tonnes.
 19. A method of ground compaction, inwhich a ground compaction apparatus, the apparatus comprising a weightedground impact body with an outer surface which reduces in width to anose, the outer surface having a plurality of first regions which taperat a first taper angle, and at least one second region between firstregions, the second region tapering at a second taper angle which isgreater than the first taper angle, is dropped on the ground to becompacted. 20-22. (canceled)